Helicobacter pylori clearance and serum gastrin and pepsinogen I concentrations in omeprazole treatment of duodenal ulcer patients

Objective: To determine which demographic factors may influence serum gastrin and pepsinogen I (PGI) levels in duodenal ulcer patients undergoing omeprazole treatment. Methods: We conducted an outpatient-based prospective study in the Veterans General Hospital, Taipei, to investigate the pharmacological effects on patients with duodenal ulcers receiving omeprazole treatment for 4 weeks. Sixty-eight patients (61 males/7 females, aged 25–73 years) with endoscopically confirmed duodenal ulcer were included. Gastrin and pepsinogen I levels were measured before and after treatment. Demographic factors including age, sex, smoking, ulcer healing and antral Helicobacter pylori colonization/clearance were analyzed, in order to measure their probable influences on serum gastrin and pepsinogen I levels. Results: Ulcer healing was seen in 92.6% of patients while 48 (70.6%) antral clearances were seen in 66 H. pylori colonized patients at the end of trial. Omeprazole monotherapy led to a marked elevation of serum gastrin (85.8 pg · ml⁻¹, SD 32.0 pg · ml⁻¹ vs 133.9 pg · ml⁻¹, SD 71.6 pg · ml⁻¹, P < 0.01), and pepsinogen I (111.0 ng · ml⁻¹, SD 36.7 ng · ml⁻¹ vs 253.6 ng · ml⁻¹, SD 64.8 ng · ml⁻¹, P < 0.01) levels when measured on day 29. Only patients showing antral H. pylori clearance exhibited an influence on the magnitude of pepsinogen I elevation following omeprazole monotherapy (143.9%, SD 67.3% vs 78.6%, SD 51.2%, P < 0.01). Moreover, the sensitivity and specificity of serum pepsinogen I variations were plotted on a receiving operating characteristic (ROC) curve. The 140% increased pepsinogen I level yielded a maximum accuracy of 80% specificity or 50% sensitivity to predict antral H. pylori clearance. Conclusion: Antral H. pylori clearance is at least partially responsible for the omeprzaole-induced hyperpepsinogenemia I. The magnitude of hyperpepsinogenemia I probably provides a non-invasive alternative for predicting H. pylori clearance. Received: 22 August 1996 / Accepted in revised form: 1 October 1998     

Variability of morphine disposition during long-term subcutaneous infusion in terminally ill cancer patients

Objective: To study the plasma concentrations of morphine and its glucuronides to assess the intra- and interindividual variability of the disposition of morphine administered by subcutaneous infusion in cancer patients. Methods: Blood samples were taken repeatedly in eight patients with severe cancer pain who were being treated with morphine (60–3000 mg per day) via chronic (8–160 days) subcutaneous infusion. Venous blood samples were collected at least weekly and, when possible, on 3 consecutive days after dose adaptation or any other major change in the patients' treatment. Concentrations of morphine and its glucuronides in plasma were measured after solid-phase extraction using a validated high-performance liquid chromatography assay. The stability of the morphine solutions was determined by repeated measurement of the concentrations of morphine and its degradation products in the solutions. Results: The morphine concentration in the infusion solutions remained unchanged during storage and infusion. The plasma concentrations of morphine and its glucuronides were within the ranges reported in the literature. There was, as expected, a large interindividual variability: from patient to patient, the mean of the normalised plasma concentrations ranged from 0.3 ng · ml⁻¹ · mg⁻¹ to 0.8 ng · ml⁻¹ · mg⁻¹ for morphine, from 1.0 ng · ml⁻¹ · mg⁻¹ to 3.1 ng · ml⁻¹ · mg⁻¹ for morphine-6-glucuronide and from 6.8 ng · ml⁻¹ · mg⁻¹ to 24.3 ng · ml⁻¹ · mg⁻¹ for morphine-3-glucuronide. Intraindividual variability was also important. The residual standard deviation of the mean normalised plasma concentrations calculated for each patient ranged from 26% to 56% for morphine, from 20% to 51% for morphine-6-glucuronide and from 20% to 49% for morphine-3-glucuronide. The normalised plasma concentrations of morphine and its glucuronides did not increase with dose or time, and no explanation for the pronounced pharmacokinetic intraindividual variability was found. Conclusion: During subcutaneous infusion of morphine, there is a large intra- and interindividual variability of the morphine disposition which could be of clinical relevance. Received: 5 August 1997 / Accepted in revised form: 8 October 1997     

Lack of pharmacokinetic interaction between ropinirole and theophylline in patients with Parkinson's disease

Objective: Ropinirole and theophylline have the potential to interact, because they use the same hepatic cytochrome P450 (CYP1A2) as their major metabolic pathway. The present study investigated the effect of steady-state oral theophylline on the pharmacokinetics of ropinirole at steady state and the effect of steady-state ropinirole on the pharmacokinetics of a single intravenous (i.v.) dose of theophylline, both in patients with idiopathic Parkinson's disease (PD). Methods: Pharmacokinetic parameters (AUC and C_max) for i.v. theophylline were compared before and after a 4-week period of oral treatment with ropinirole (2 mg t.i.d.) in 12 patients with PD. Patients were then maintained at this dose of ropinirole, and oral theophylline was co-administered at doses of up to 300 mg b.i.d. The parameters AUC, C_max and t_max for ropinirole were compared before, during and after oral theophylline co-treatment. Results: Co-administration of ropinirole did not significantly change the pharmacokinetics of i.v. theophylline (mean AUC with and without ropinirole: 68.6 μg · h⁻¹ · ml⁻¹ and 70.0 μ· h⁻¹ · ml⁻¹, respectively; mean C_max with and without ropinirole: 11.07 μ g · ml⁻¹ and 11.83 μg · ml⁻¹, respectively). Similarly, there were no significant changes in ropinirole pharmacokinetics when the drug was co-administered with oral theophylline (mean AUC for ropinirole with and without theophylline: 21.91 ng · h⁻¹ · ml⁻¹ and 22.09 ng · h⁻¹ · ml⁻¹, respectively; mean C_max for ropinirole with and without theophylline: 5.65 ng · ml⁻¹ and 5.54 ng · ml⁻¹, respectively; median t_max for ropinirole with and without theophylline: 2.0 h and 1.5 h, respectively). Conclusion: These results suggest a lack of significant pharmacokinetic interaction between the two drugs at current therapeutic doses. Received: 10 August 1998 / Accepted in revised form: 27 January 1999     

Lack of a pharmacokinetic interaction between atovaquone and proguanil

Objective: To assess the magnitude of the putative effect of atovaquone on the pharmacokinetics of proguanil and to determine whether the pharmacokinetics of atovaquone are affected by concomitant administration of proguanil, with both drugs administered for 3 days to healthy adult volunteers. Methods: This was an open-label, randomized, three-way cross-over study, in which 18 healthy volunteers received 400 mg proguanil, 1000 mg atovaquone and 1000 mg atovaquone + 400 mg proguanil. Each treatment was given once daily for 3 days with a 3-week wash-out period between each occasion. For the assay of proguanil, cycloguanil and atovaquone, blood was sampled before dosing and at regular intervals over 8 days when proguanil was given, and over 17 days when atovaquone was given. Results: The geometric mean of the area under the atovaquone plasma concentration-time curve calculated from 0 to 24 h after the last dose (AUC_0→24h) was 180 μg · ml⁻¹ · h following administration of atovaquone alone and 193 μg · ml⁻¹ · h following atovaquone with proguanil. The geometric mean AUC_0→24h for proguanil was 6296 ng · ml⁻¹ · h after proguanil alone and 5819 ng · ml⁻¹ · h following proguanil with atovaquone. The corresponding values for the metabolite cycloguanil were 1297 ng · ml⁻¹ · h and 1187 ng · ml⁻¹ · h, respectively. The geometric mean elimination half-life (t_1/2) of atovaquone was 57.1 h when given alone and 59.0 h when administered together with proguanil. The corresponding geometric mean values of t_1/2 for proguanil were 13.7 h and 14.5 h. Exploratory statistical analysis showed no important gender effects on the pharmacokinetics of atovaquone, proguanil, or cycloguanil. Conclusion: The pharmacokinetics of atovaquone and proguanil and its metabolite, cycloguanil, were not different when atovaquone and proguanil were given alone or in combination. Received: 14 October 1998 / Accepted in revised form: 8 February 1999     

Temperature dependency of the release and bioavailability of nicotine from a nicotine vapour inhaler; in vitro/ in vivo correlation

Objective: To investigate the temperature dependency of the dose released and the plasma levels of nicotine from a vapour inhaler. Methods: In an open, randomised, three-way cross-over pharmacokinetic study 18 healthy subjects inhaled nicotine for 20 min (80 inhalations) every hour for 10 h (11 administrations) at three different environmental temperatures: 20°, 30° and 40 °C. In the in vitroexperiment, 5, 10, 15 and 20 l air were forced through the inhaler. With a 15 l air volume, the average amount of nicotine released was 1.44, 3.49, 4.80 and 6.99 mg at 10 °C, 22 °C, 29 °C and 40 °C, respectively. The maximum dose released at the highest temperature (40 °C) and the largest air volume investigated (20 l) was approximately 7.5 mg. Results: In vivo peak plasma levels obtained at 30° and 40 °C were 29.7 and 34.0 ng · ml⁻¹, compared with 22.5 ng · ml⁻¹ at ambient room temperature (20 °C). At 20 °C, the area under the plasma concentration–time curve (AUC) of the last dosing interval was 20.5 ng · ml⁻¹ · h. At 30 °C and 40 °C, the AUCs were 26.5 and 30.3 ng · ml⁻¹ · h, respectively. The results thus showed a mean increase of the in vivo AUC by 29% at 30 °C and by 48% at 40 °C compared with the AUC at 20 °C. These increases should be compared to the in vitro results, showing a mean increase of 59% and 122%, respectively, at 30° and 40 °C. The in vitro results also showed that a relatively larger fraction of the dose was released into the first 5 l of air at the higher temperatures, at 40 °C, about 50% of the total amount released into 20 l. Conclusion: It was concluded that the in vitro/in vivo discrepancy was most probably due to increased aversive effects at elevated temperatures, causing the subjects to inhale smaller puff volumes. Further, the inhaler would not produce nicotine plasma levels exceeding those achieved following cigarette smoking, even in a hot climate. Received: 20 September 1996 / Accepted in revised form: 5 March 1997     

Pharmacokinetics of cloxacillin in patients undergoing hip or knee replacement

Objective: The pharmacokinetics of cloxacillin was investigated in 14 men and 24 women undergoing cemented hip (n = 19; age range 56–90) or knee replacement surgery (n = 19; age range 51–84) for osteoarthritis. Cloxacillin 1 g was given intravenously as a bolus dose at the induction of anesthesia, and plasma samples and urine were collected for 6 h. Drug levels were determined using HPLC. Results: Preoperative serum creatinine levels were 84 μmol · l⁻¹ in hip patients and 72 μmol · l⁻¹ in knee patients. The calculated values for creatinine clearance were 63 and 85 ml · min⁻¹ · 1.73 m⁻², respectively. Total clearance of cloxacillin was 134 ml · min⁻¹ · 1.73 m⁻² in eighteen evaluated patients undergoing hip replacement, and 162 ml · min⁻¹ · 1.73 m⁻² in eighteen patients undergoing knee surgery. Renal clearance was 72 and 79 ml · min⁻¹ · 1.73 m⁻², respectively. Non-renal clearance was 57 ml · min⁻¹ · 1.73 m⁻² in hip patients and 77 ml · min⁻¹ · 1.73 m⁻² in knee patients. Renal clearance of cloxacillin correlated with the estimated creatinine clearance (r = 0.652). Although women received higher doses than men (median 2.02 vs 2.32 mmol · 1.73 m⁻²), there were no sex differences in clearance corrected for body surface area. Conclusion: Total clearance of cloxacillin was lower in patients undergoing hip replacement than in patients undergoing replacement of the knee, but there was no difference between men and women. Received: 7 May 1996 / Accepted in revised form: 15 October 1996     

Pharmacokinetics and tolerability of oral iloprost in thromboangiitis obliterans patients

Objective: Iloprost is a potent PGI₂ mimetic, which has been shown to be therapeutically effective in several vascular disorders. Due to its rapid clearance from the central compartment, iloprost is administered mainly by i.v. infusion, which limits its use to hospitalized patients. In order to improve pharmacotherapeutic use of this PGI₂ mimetic, an oral extended-release (ER) dosage form has been developed, which should mimic plasma level profiles as observed after i.v. infusion and serve as a therapeutic equivalent. Methods: This trial was performed to investigate the tolerability and pharmacokinetics of iloprost administered perorally, compared with i.v. infusion, in 12 patients suffering from thromboangiitis obliterans (TAO). A dose titration was carried out for 1 week with i.v. iloprost, followed by a p.o. titration and treatment phase of 3 weeks' duration. Pharmacokinetics was investigated at the individually tolerated dose levels; i.e., on days 5–7 (i.v. infusion at 2, 2.5 and 3 ng · kg⁻¹ · min⁻¹), and twice during p.o. treatment after b.i.d. administration of 50, 100, 150, 200 or 300 μg. Results: Individual tolerability of iloprost varied: 7 patients out of 12 tolerated the maximum i.v. dose of 3 ng · kg⁻¹ · min⁻¹; six tolerated the maximum oral dose of 600 μg. No patients withdrew from the study due to adverse events. Flush and headache were the most common adverse events and seemed to be related to the study drug. After i.v. infusion of iloprost, dose-normalized (3 ng · kg⁻¹ · min⁻¹), steady-state plasma levels were 260 pg · ml⁻¹. Terminal half-life was 0.57 h. Total clearance ranged from 8 to 17 ml · min⁻¹ · kg⁻¹. Peroral administration of the ER formulation resulted in dose-dependent C_max and AUC values. AUC values of the first and second daily dose interval, i.e., 0–5 h and 5–11 h after first dosing, were almost identical. Absolute bioavailability was 24%, with the exception of two patients who tolerated only 50 μg b.i.d. and exhibited a bioavailability of approx. 60%. The AUC values observed in weeks 2 and 4 were identical, demonstrating low day-to-day variability of iloprost plasma level profiles in TAO patients. Conclusion: Based upon pharmacokinetic data, the ER formulation provides an equivalent to the i.v. infusion of iloprost and broadens the range of therapy to non-hospitalized patients. The availability of capsules with 50 and 100 μg iloprost enables individual dose titration and pharmacotherapy. Beneficial effects, as observed with i.v. iloprost in TAO patients, should therefore be achievable by peroral pharmacotherapy using the new ER formulation. Received: 18 July 1996 / Accepted in revised form: 2 April 1997     

Determination of the relative bioavailability of nedocromil sodium to the lung following inhalation using urinary excretion

Objective: To determine the effects of cimetidine on the steady-state pharmacokinetics and pharmacodynamics of atorvastatin, a 3-hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitor. Methods: Twelve healthy subjects participated in a randomized two-way crossover study. Each subject received atorvastatin 10 mg every morning for 2 weeks and atorvastatin 10 mg every morning with cimetidine 300 mg four times a day for 2 weeks, separated by a 4-week washout period. Steady-state pharmacokinetic parameters (based on an enzyme inhibition assay) and lipid responses were compared. Results: Pharmacokinetic parameters and lipid responses were similar following administration of atorvastatin alone and atorvastatin with cimetidine. Mean values for C_max (the maximum concentration) were 5.11 ng · eq · ml⁻¹ and 4.54 ng eq · ml⁻¹, for t_max (the time to reach maximum concentration) 2.2 h and 1.3 h, for AUC_0–24 (area under the concentration-time curve from time 0 h to 24 h) 58.6 ng eq · h · ml⁻¹ and 58.5 ng eq · h · ml⁻¹, and for t_1/2 (terminal half-life) 10.1 h and 17.0 h, respectively, following administration of atorvastatin alone and atorvastatin with cimetidine. Following treatment with atorvastatin alone and atorvastatin with cimetidine, mean values for the percentage change from baseline for total cholesterol were −29.5% and −29.9%, for low-density lipoprotein (LDL) cholesterol −41.0% and −42.6%, for high-density lipoprotein (HDL) cholesterol 6.3% and 5.8%, and for triglycerides −33.8% and −25.8%, respectively. Conclusions: The rate and extent of atorvastatin absorption and the effects of atorvastatin on LDL-cholesterol responses are not influenced by coadministration of cimetidine. Received: 17 February 1997 / Accepted in revised form: 3 November 1997     

Population analysis of the non-linear red blood cell partitioning of draflazine following various infusion durations

Objective: The pharmacokinetics and non-linear red blood cell partitioning of the nucleoside transport inhibitor draflazine were investigated in 19 healthy male and female subjects (age range 22–55 years) after a 15-min i.v. infusion of 1 mg, immediately followed by infusions of variable rates (0.25, 0.5 and 1 mg · h⁻¹) and variable duration (2–24 h). Methods: The parameters describing the capacity-limited specific binding of draflazine to the nucleoside transporters located on erythrocytes were determined by NONMEM analysis. The red blood cell nucleoside transporter occupancy of draflazine (RBC occupancy) was evaluated as a pharmacodynamic endpoint. Results: The population typical value for the dissociation constant K _d (%CV) was 0.648 (12) ng · ml⁻¹ plasma, expressing the very high affinity of draflazine for the erythrocytes. The typical value of the specific maximal binding capacity B_max (%CV) was 155 (2) ng · ml⁻¹ RBC. The interindividual variability (%CV) was moderate for K _d (38.9%) and low for B_max (7.8%). As a consequence, the variability in RBC occupancy of draflazine was relatively low, allowing the justification of only one infusion scheme for all subjects. The specific binding of draflazine to the red blood cells was a source of non-linearity in draflazine pharmacokinetics. Steady-state plasma concentrations of draflazine virtually increased dose-proportionally and steady state was reached at about 18 h after the start of the continuous infusion. The t_1/2βaveraged 11.0–30.5 h and the mean CL from the plasma was 327 to 465 ml · min⁻¹. The disposition of draflazine in whole blood was different from that in plasma. The mean t_1/2β was 30.2 to 42.2 h and the blood CL averaged 17.4–35.6 ml · min⁻¹. Conclusion: Although the pharmacokinetics of draflazine were non-linear, the data of the present study demonstrate that draflazine might be administered as a continuous infusion over a longer time period (e.g., 24 h). During a 15-min i.v. infusion of 1 mg, followed by an infusion of 1 mg · h⁻¹, the RBC occupancy of draflazine was 96% or more. As the favored RBC occupancy should be almost complete, this dose regimen could be justified in patients. Received: 6 February 1997 / Accepted in revised form: 12 May 1997     

The area under the plasma concentration–time curve for oral midazolam is 400-fold larger during treatment with itraconazole than with rifampicin

Objective: To determine the effects of treatment with itraconazole and rifampicin (rifampin) on the pharmacokinetics and pharmacodynamics of oral midazolam during and 4 days after the end of the treatment. Methods: Nine healthy volunteers received itraconazole (200 mg daily) for 4 days and, 2 weeks later, rifampicin (600 mg daily) for 5 days. In addition, they ingested 15 mg midazolam before the first treatment, 7.5 mg on␣the␣last day of itraconazole administration, and 4 days␣later,␣and 15 mg 1 day and 4 days after the last dose␣of␣rifampicin.␣The disposition of midazolam and its α-hydroxy metabolite was determined and its pharmacodynamic effects were measured. Results: During itraconazole treatment, or 4 days after, α-hydroxymetabolite the dose-corrected area under the plasma midazolam concentration–time curve (AUC_0–∞) was 8- or 2.6-fold larger than that before itraconazole (i.e. 1707 or 695 versus 277 ng · h · ml⁻¹), respectively. One day after rifampicin treatment, the AUC_0–∞ of midazolam was 2.3% (i.e. 4.4 ng · h · ml⁻¹) of the before-treatment value and only 0.26% of its value during itraconazole treatment; 4 days after rifampicin, the AUC_0–∞ was still only 13% (i.e. 27.1 ng · h · ml⁻¹) of the before-treatment value. The peak concentration and elimination half-life of midazolam were also increased by itraconazole and decreased by rifampicin. The ratio of plasma α-hydroxymidazolam to midazolam was greatly decreased by itraconazole and increased by rifampicin. In addition, the effects of midazolam were greater during itraconazole and smaller 1 day after rifampicin than without treatment. Conclusion: Switching from inhibition to induction of cytochrome P450 3A (CYP3A) enzymes causes a very great (400-fold) change in the AUC of oral midazolam. During oral administration of CYP3A substrates that undergo extensive first-pass metabolism, similar changes in pharmacokinetics are expected to occur when potent inhibitors or inducers of CYP3A are added to the treatment. After cessation of treatment with itraconazole or rifampicin, the risk of significant interaction continues up to at least 4 days, probably even longer. Received: 17 June 1997 / Accepted in revised form: 16 October 1997     

Penetration of ciprofloxacin, norfloxacin and ofloxacin into the aqueous humour of patients by different topical application modes

Objectives: A prospective study was undertaken to determine the transcorneal penetration of three topically applied fluoroquinolones into aqueous humour. Methods: Two hundred and twenty-four patients undergoing cataract extraction received 0.3% ciprofloxacin, norfloxacin or ofloxacin eye drops by two different administration modes with different frequencies and intervals of application. At the beginning of cataract extraction (0.5–3 h after the last drop), 50–100 μl aqueous fluid was aspirated from the anterior chamber and immediately stored at −80 °C. Antibiotic concentrations were measured using high-performance liquid chromatography. Results: Generally, topical ofloxacin and ciprofloxacin yielded aqueous humour levels higher than topical norfloxacin. The highest concentrations of all tested fluoroquinolones were measured after using an application mode, in which one drop was given every 15 min between 0600 hours and 0800 hours, prior to operation. When applied by this mode, ciprofloxacin achieved a mean aqueous level of 0.380 (±0.328) μg · ml⁻¹ (range 0.033–1.388 μg · ml⁻¹), norfloxacin 0.182 (0.118) μg · ml⁻¹ (range 0.038–0.480 μg · ml⁻¹) and ofloxacin 0.564 (0.372) μg · ml⁻¹ (range 0.064–1.455 μg · ml⁻¹). These mean concentrations were above the minimum inhibitory concentration (MIC₉₀), concentrations required for inhibition of 90% of pathogen strains in vitro of gram-negative bacteria, such as Proteus mirabilis and Escherichia coli. Therapeutic values above the MIC₉₀ of Staphylococcus epidermidis, the pathogen causing eye infections most frequently, were reached by 67.5% of patients after ofloxacin and by 41% after ciprofloxacin, but never after norfloxacin treatment. Conclusion: Of the currently available topical fluoroquinolones, ofloxacin achieved the highest aqueous humour concentration. This fluoroquinolone may be an useful ophthalmic agent for topical antibacterial management, but it does not seem to be prophylactically effective against Streptococcus pneumoniae or Pseudomonas aeruginosa. Received: 22 April 1997 / Accepted: 8 June 1997     

Pharmacokinetics and safety of candesartan cilexetil in subjects with normal and impaired liver function

Objective: The influence of liver disease on the pharmacokinetics of candesartan, a long-acting selective AT₁ subtype angiotensin II receptor antagonist was studied. Methods: Twelve healthy subjects and 12 patients with mild to moderate liver impairment received a single oral dose of 12 mg of candesartan cilexetil on day 1 and once-daily doses of 12 mg on days 3–7. The drug was taken before breakfast. Serial blood samples were collected for 48 h after the first and last administration on days 1 and 7. Serum was analyzed for unchanged candesartan by HPLC with UV detection. Results: The pharmacokinetic parameters on days 1 and 7 revealed no statistically significant influence of liver impairment on the pharmacokinetics of candesartan. Following single dose administration on day 1, the␣mean␣C_max was 95.2 ng · ml⁻¹ in healthy subjects and 109 ng · ml⁻¹ in the patients. The AUC_0−∞ was␣909 ng.h · ml⁻¹ in healthy volunteers and 1107 ng.h · ml⁻¹ in patients and the elimination half-life was 9.3 h in healthy volunteers and 12 h in the patients. At steady state on day 7, mean C_max values were similar in both groups (112 vs 116 ng · ml⁻¹); the AUC_τ was 880 ng.h · ml⁻¹ in healthy subjects and 1080 ng.h · ml⁻¹ in patients while the elimination half-life was 10 h in healthy subjects and 12 h in the patients with liver impairment. The AUC_0−∞ on day 1 was almost identical to the AUC_τ on day 7. A moderate drug accumulation of 20%, which does not require a dose adjustment, was observed following once-daily dosing in both groups. No serious or severe adverse events were reported. Conclusion: Mild to moderate liver impairment has no clinically relevant effect on candesartan pharmacokinetics, and no dose adjustment is required for such patients. Received: 24 November 1997 / Accepted in revised form: 18 February 1998     

Effect of rifampicin on the pharmacokinetics of itraconazole in normal volunteers and AIDS patients

Objective: To investigate the effects of rifampicin on the pharmacokinetics of itraconazole in humans. Methods: Our study was conducted with six healthy normal volunteers and three AIDS patients. All subjects received a 200 mg single dose of oral itraconazole on day 1 and day 15 and 600 mg of oral rifampicin once daily from day 2 to day 15. Itraconazole pharmacokinetics studies were carried out on day 1 (phase 1) and day 15 (phase 2). The limit of detection for itraconazole concentration was 16 ng · ml^–1. Results: Concentrations itraconazole were higher when it was administered alone than when it was administered with rifampicin. Coadministration of rifampicin resulted in undetectable levels of itraconazole in all subjects except one normal volunteer. The mean AUC_0–24 was 3.28 vs 0.39 μg · h · ml⁻¹ in phase 1 and 2, respectively, in healthy normal volunteers. Therefore, the estimated minimum decrease of the mean AUC_0–24 of itraconazole in phase 2 was approximately 88% compared with phase 1. The mean AUC_0–24 was 1.07 vs 0.38 μg · h · ml^–1 in phase 1 and 2, respectively, in AIDS patients. Therefore, the estimated minimum decrease of the mean AUC_0–24 of itraconazole in phase 2 was approximately 64% compared with phase 1. Conclusion: Rifampicin has a very strong inducing effect on the metabolism of itraconazole, so that these two drugs should not be administered concomitantly. Received: 2 September 1997/Accepted in revised form: 16 December 1997     

Pharmacokinetics and pharmacodynamics of candesartan cilexetil in patients with normal to severely impaired renal function

Objective: We studied the pharmacokinetics and pharmacodynamics of single and multiple doses of candesartan cilexetil 8 mg per day in hypertensive patients with different degrees of renal function impairment. Candesartan is an angiotensin II subtype 1 (AT1) receptor antagonist that is administered orally as candesartan cilexetil which is converted in the active compound. Methods: Twenty-three patients were included, divided into groups according to creatinine clearance (cr cl. group A >60 nl · min⁻¹ · 1.73 m⁻², group B 30–60 ml · min⁻¹ · 1.73 m⁻² and group C 15–30 ml · min⁻¹ · 1.73 m⁻²). Results: Trough serum concentrations of candesartan were higher in group C compared with group A. The values did not increase after multiple dosing, indicating absence of accumulation. There was a significant negative correlation between the area under the concentration-time curve extrapolated to time infinity (AUC_inf) and the glomerular filtration rate (GFR) indicating a lower renal clearance of candesartan in patients with impaired renal function. The onset of haemodynamic and hormonal effects was gradual. During the single-dose study blood pressure as well as plasma renin activity (PRA) and angiotensin II were unchanged at peak. At day 5 of the multiple-dose study blood pressure was lower and both PRA and angiotensin II were higher compared with baseline. Conclusion: Although serum trough levels increased during repeated administration and half-life was higher in patients with impaired renal function, candesartan cilexetil at a dose of 8 mg per day does not lead to drug accumulation in these patients. This dose is effective in lowering blood pressure and appears to be suitable for patients with renal function impairment. Received: 3 August 1998 / Accepted in revised form: 19 October 1998     

Effects of dopamine on veins in humans: comparison with noradrenaline and influence of age

Objective: To compare the venoconstricting effect of dopamine with that of noradrenaline and to investigate the influence of age on the responsiveness to dopamine in human subjects. Methods: In eight young and eight elderly male subjects, increasing doses of dopamine or noradrenaline were infused into a dorsal hand vein and its diameter was measured using a linear variable differential transformer. Results: There was no significant difference between the maximum venoconstriction (E_max) for dopamine and that for noradrenaline. The infusion rate to induce 50% of E_max (ED₅₀) for dopamine in the young and elderly subjects was 363 ng · min⁻¹ and 352 ng · min⁻¹, and the ED₅₀ for noradrenaline was 40.7 ng · min⁻¹ and 43.8 ng · min⁻¹, respectively. Neither in the E_max nor in the ED₅₀ for these drugs were there significant differences between the young and elderly subjects. Conclusion: The venoconstricting effect of dopamine is 5–20 times less than that of noradrenaline, and aging does not influence the responsiveness to dopamine and noradrenaline in human subjects. Received: 29 August 1997 / Accepted in revised form: 5 February 1998     

Age-dependent differences in the anticoagulant effect of phenprocoumon in patients after heart valve surgery

Objective: An enhanced response to warfarin and an increased risk of major bleeding has been observed in older patients. The reason for this increase in sensitivity remains unknown. It could be due to pharmacodynamic reasons, pharmacokinetic reasons, or both. Methods: We therefore followed an anticoagulant regimen with phenprocoumon in 19 older (76 years) and 19 younger patients (50 years) following heart valve replacement. INR values were determined frequently. At the 4th and around the 24th day after starting treatment with phenprocoumon, we also measured the total and unbound plasma concentration of phenprocoumon. Results: The dose requirement to obtain the desired anticoagulant effect was significantly lower in the older patients than in the younger patients (26.3 vs. 37.3 μg · kg⁻¹ · day⁻¹). The total plasma concentration (2.19 vs. 2.43 μg · ml⁻¹), the percentage unbound drug in the plasma (0.61 vs. 0.64%) and the unbound plasma concentration (13.8 vs. 15.1 ng · ml⁻¹) did not differ significantly between older and younger patients. The dose-adjusted INR (INR/dose) was higher in the older patients (110 vs. 67) but the INR adjusted for the unbound plasma concentration (INR/C_uss) which reflects the intrinsic sensitivity to the drug, was not significantly different (192 vs. 173). However, the older patients had an about 30% significantly lower metabolic clearance based on unbound drug (84 vs. 115 ml · kg⁻¹ · h⁻¹). Conclusions: Older patients (> 70 years) require a dose approximately 30% lower than younger patients (< 160␣years). Pharmacokinetic reasons (reduced metabolic clearance) are mainly responsible for the lower dose requirement of the older patients after heart valve surgery. Received: 23 August 1996 / Accepted November 11 1996     

Renal handling of drugs in the healthy elderly Creatinine clearance underestimates renal function and pharmacokinetics remain virtually unchanged

Objective: It is commonly assumed that renal function, and in parallel the excretion of drugs, is considerably reduced in the elderly. Endogenous creatinine clearance or indirect estimates of this parameter are generally recommended for adapting drug dosage. The present study evaluates the validity of both assumptions. Methods: We compared pharmacokinetics (and pharmacodynamics) of 50 mg atenolol, 800 mg piracetam and 25 mg hydrochlorothiazide plus 50 mg triamterene in ten healthy young [25 (2) years] and 11 healthy elderly subjects [68 (5) years]. Inulin (C_in) and para-aminohippurate [PAH (C_PAH)] clearance (infusion clearance technique), endogenous (C_Cr) and calculated (Cockroft-Gault) creatinine clearance, analysis of drugs and their metabolites (HPLC), were performed. Renal haemodynamics and the pharmacokinetics of β-adrenergic blocking agent, diuretics and the nootropic agent piracetam, respectively, were measured on separate days. Results: C_in was significantly (P < 0.01) lower in the healthy elderly subjects [104 (12) vs 120 (14) ml · min⁻² · 1.73 m⁻² in the young], but remained within the normal range (>90 ml · min⁻² · 1.73 m⁻²). In contrast, C_Cr was even lower in healthy elderly subjects [95 (24) vs 121 (20) ml · min⁻¹ in the young], and the Cockroft-Gault clearance underestimated true glomerular filtration rate (GFR) even more seriously [74 (17) vs 122 (16) ml · min⁻¹]. For atenolol the mean area under the curve (AUC) was similar in both groups [3.16 (0.48) μg · h⁻¹ · ml⁻¹ in the elderly vs 3.01 (0.30) in the young], as was the mean maximal plasma concentration [0.42 (0.07) vs 0.44 (0.06) μg · ml⁻¹], but the proportion of the drug excreted in urine was marginally (P < 0.025) lower in the elderly. Similar results were obtained for hydrochlorothiazide, whereas no marked differences between the groups were found for triamterene and its metabolite. Furthermore, the pharmacodynamic action of diuretics was not significantly altered in the elderly. Conclusions: The true GFR of the healthy elderly remains within the normal range and is underestimated by creatinine clearance and more so by its surrogate (Cockroft-Gault clearance). In parallel, pharmacokinetics of renally excreted drugs are not affected in the healthy elderly to a clinically significant extent. For drugs with a narrow therapeutic window, indirect estimates of GFR appear to be an unreliable means for calculating correct dosage in the elderly. Received: 2 April 1998 / Accepted in revised form: 19 October 1998     

Effect of itraconazole on the pharmacokinetics and pharmacodynamics of zolpidem

Objective: Zolpidem is a short-acting␣imidazopyridine hypnotic which is biotransformed in humans mainly by CYP3A4. Itraconazole strongly interacts with many substrates of CYP3A4 such as midazolam and triazolam. In this study, the effect of itraconazole on the pharmacokinetics and pharmacodynamics of zolpidem was investigated to uncover a possible clinically significant interaction. Methods: In a randomized cross-over study with two phases, ten healthy volunteers took either 200 mg itraconazole or placebo once daily for 4 days. A single oral dose of 10 mg zolpidem was given on day 4. Plasma drug concentrations were measured up to 17 h and effects of zolpidem up to 9 h after the ingestion of zolpidem. Results: Itraconazole had no marked effects on the pharmacokinetics of zolpidem; the total area under the plasma zolpidem concentration–time curve (AUC_0–∞) was 34% larger during the itraconazole phase (759 ng · h · ml⁻¹) than during the placebo phase (567 ng · h · ml⁻¹). Exophoria of the eyes by the Maddox wing test was significantly increased by itraconazole, but the results of the digit symbol substitution test, critical flicker fusion test, postural sway tests and the visual analogue scale tests for subjective drowsiness and overall drug effect did not differ between the phases. Conclusion: The pharmacokinetics and pharmacodynamics of zolpidem were not remarkably affected by itraconazole in healthy volunteers. Therefore, unlike triazolam, for example, zolpidem can be used in normal or nearly normal doses together with itraconazole and probably also with other CYP3A4 inhibitors. Received: 30 September 1997 / Accepted in revised form: 12 January 1998     

Improved penetration of aminoglycosides and fluoroquinolones into the aqueous humour of patients by means of Acuvue contact lenses

Objectives: In order to improve the penetration of topically applied drugs in ophthalmology, the suitability of hydrophilic contact lenses (Acuvue, Vistacon, power −1.0 D) as a drug delivery system for antibiotics was tested. A prospective study was undertaken to determine the transcorneal penetration of five topically applied aminoglycosides and fluoroquinolones into the aqueous humour of patients. Methods: Two hundred and sixty-five patients undergoing cataract extraction received 0.3% gentamicin, kanamycin, tobramycin, ciprofloxacin or ofloxacin solution by two different modes of administration: either as eye drops (nine drops every 15 min, starting 2 h prior to surgery) or by means of a drug delivery system (Acuvue contact lenses soaked for 1 h in eye drop solution without preservatives, 1–5 h prior to surgery). At the beginning of cataract extraction, 50–100 μl aqueous fluid was aspirated from the anterior chamber and immediately stored at −80 °C. Antibiotic concentrations were measured using fluorescence polarisation immuno-assays (aminoglycosides) or high-performance liquid chromatography (fluoroquinolones). Results: After soaking for 1 h in 0.3% eye drop solutions, Acuvue contact lenses released about 190–250 μg aminoglycoside and ofloxacin and 1000 μg ciprofloxacin. These amounts are considerably lower or in the same order of magnitude than obtained with application of eye drops (1350 μg). From the aminoglycosides tested, only gentamicin and tobramycin, but not kanamycin, were able to penetrate into the aqueous humour of patients. After the wearing of antibiotic-soaked lenses, mean aqueous humour concentrations were higher than after the use of eye drops. This difference reached significance in tobramycin (1.09 (1.30) μg · ml⁻¹ vs 0.49 (0.79) μg · ml⁻¹), ciprofloxacin (1.23 (0.60) μg · ml⁻¹ vs 0.38 (0.33) μg · ml⁻¹) and ofloxacin (5.55 (2.53) μg · ml⁻¹ vs 0.56 (0.37) μg · ml⁻¹). The percentage of patients with aqueous humour concentration above the MIC₉₀ of Staphylococcus epidermidis, the most common cause of postoperative endophthalmitis, was 92% and 100% after wearing ciprofloxacin- or ofloxacin-soaked lenses, respectively. Conclusion: Gentamicin and tobramycin penetrated into the aqueous humour of patients, whereas kanamycin was not able to overcome the corneal barrier. Acuvue contact lenses soaked in 0.3% eye drop solutions can release sufficient amounts of gentamicin, ciprofloxacin and ofloxacin to produce bacteriostatic concentrations in the humor aquosus. Acuvue contact lenses can be recommended as a drug delivery system for fluoroquinolones. Received: 15 October 1998 / Accepted in revised form: 16 December 1998     

Clinical pharmacokinetics of ciprofloxacin in patients with major burns

Objective: To better master the use of ciprofloxacin (CPF) in burn patients, a clinical study, including pharmacokinetics in serum and urine, was undertaken in a pathophysiologically homogeneous population of major-burn subjects. Methods: Twelve major-burn patients who were infected with Pseudomonas aeruginosa, enterobacteria and gram-positive cocci, received CPF (600 mg t.i.d.). The mean body surface area affected by third-degree burns was 31.8 ± 14.5%. Two series of blood samples were drawn after the first and seventh doses; urine was collected during the first infusion. Levels of CPF in serum and urine were measured by means of high-performance liquid chromatography. A non-compartmental method was used for kinetic and graphic analysis of concentration–time pairs. Results: No adverse effects were noted. Trough concentrations measured on day 3 (mean ± SD) were above the minimum inhibitory concentration (MIC) for the organism responsible for infection; i.e., 2.0 ± 1.2 μg · ml⁻¹, and maximum concentrations were high 9.9 ± 3.4 μg · ml⁻¹. An area under the concentration–time curve (AUC)/MIC ratio above 125 SIT⁻¹ (where SIT is the serum inhibitory titer), which has been strongly correlated with clinical response and time to bacterial eradication, was achieved in 11 patients with a MIC of 0.5 μg · ml⁻¹. There was a statistically significant difference between C_min and AUC determined on day 1 and day 3. In contrast to healthy volunteers, CPF clearance rates were notably decreased. Conclusion: The pharmacokinetics of CPF was altered in major-burn patients. The recommended dosage regimen for administration of CPF, i.e. 600 mg t.i.d. shows no adverse effects and a good microbiological efficacy. Received: 13 October 1998 / Accepted in revised form: 8 June 1999